The processes involved in decomposition during the continuous heating and tempering of quenched two-phase titanium alloys VT3-1, VT8 and VT23 are investigated by means of X-ray crystallographic and high-temperature diffraction analyses, measurement of the temperature dependencies of Young's modulus and hardness, and mechanical tests. Decomposition depends on alloying of the high-temperature beta phase, and that in turn depends on the temperature to which the alloy is heated before quenching.